Crossover spinous process implant

ABSTRACT

A device intended for the treatment of spinal stenosis. This device is an inter-spinous spacer that is introduced through a single posterior incision. It uses a single piece insertion technique with a unilateral approach. The surgeon does not need to access the opposite side of the spinous process. It allows the user infinite adjustability in distraction height with a single locking mechanism.

BACKGROUND OF THE INVENTION

The leading cause of lower back pain arises from rupture or degenerationof lumbar intervertebral discs. Pain in the lower extremities can becaused by the compression of spinal nerve roots by a bulging disc, whilelower back pain is caused by collapse of the disc and by the adverseeffects of articulation weight through a damaged, unstable vertebraljoint.

In some cases, when a patient having a collapsed disc moves in extension(e.g., leans backward), the posterior portion of the annulus fibrosis orthe ligamentum flavum may further compress and extend into the spinalcanal. This condition, called “spinal stenosis”, narrows the spinalcanal and causes impingement of tissue upon the spinal cord, therebyproducing pain.

There have been numerous attempts to provide relief for theseafflictions by providing a spacer that inserts between adjacent spinousprocesses present in the posterior portion of the spinal column. Thisspacer essentially separates the upper spinous process from the lowerspinous process, thereby relieving stenosis. In general, theseinterspinous implants are adapted to allow flexion movement in thepatient, but resist or limit extension.

There are numerous publications disclosing interspinous process spacershaving a strut-like body disposed between the spinous processes. See,for example, U.S. Pat. No. 6,451,019; U.S. Pat. No. 6,451,020; U.S. Pat.No. 6,652,527; U.S. Pat. No. 7,201,751, US Patent Publication No.2005-0240182, US Patent Publication No. 2007-0203495, US PatentPublication No. 2008-0033445, US Patent Publication No. 2008-0058941, USPatent Publication No. 2008-006586, US Patent Publication No.2008-0086212, US Patent Publication No. 2008-0167656, and US PatentPublication No. 2008-0288075.

US Patent Publication No. 20080167655 (Wang) discloses devices, toolsand methods for minimally invasive implantation and distraction betweenspinous processes for treatment of spinous disorders. Wang discloses aninterspinous implant device for distracting at least one pair ofadjacent spinous processes includes a main body including a shaft havinga longitudinal axis; and first and second parallel arms extendingtransversely from the main body, wherein at least one of the first andsecond parallel arms is slidably mounted with respect to the shaft. Theparallel arms are configured and dimensioned to extend laterally fromboth sides of the spinous processes when implanted therebetween and tobe inserted between the spinous processes laterally from a single sidethereof. The parallel arms are variably positionable between a closedconfiguration, in which the parallel arms are positioned close to or incontact with one another, to facilitate insertion of the parallel armsbetween the adjacent spinous processes, and an open configuration, inwhich the parallel arms are separated from one another.

US Patent Publication No. 2007-0162000 (Perkins) discloses an adjustablespacing device configured to be placed between the spinous processes ofat least two adjacent vertebrae and a method of using the device totreat spinal stenosis by restricting extension and allowing normalflexion of adjacent vertebrae relative to one another. Perkins disclosesan implant having a horizontal member attached to two legs, one on eachside of the spinous process.

US Patent Publication No. 2008-0177271 (Yeh) discloses an implant havinga center axle for rotation of the two pieces during insertion. Yehdiscloses an interspinous process distraction device including a maledistraction element and a female distraction element, which both have aclamping portion for fixedly pushing and rejecting the interspinousprocesses and also respectively have a first connecting portion and asecond connecting portion connected at the other end of the clampingportion. Here, the first connecting portion and the second connectingportion are paired for blocking with each other so as to form theinterspinous process distraction device capable of having an oppositerotation. Besides, through clamping two interspinous processes whichstress the nerve by the male distraction element and the femaledistraction element and rotating them to oppositely rotate, the twointerspinous processes can therefore be moved to be in alignment as thenormal condition.

U.S. Pat. No. 5,393,036 (Sheridan) discloses an implant driven with ascrew or threads to create distraction.

U.S. Pat. No. 5,496,318 (Howland) discloses an implant having an H-shapeor belt to secure the implant. Howland discloses a spinal fixationdevice and method for the stabilization of the spine after surgicalprocedures such as those related to degenerative disc diseases. Thedevice comprises a spacer, which is placed between adjacent vertebraewhen installed and a locking mechanism attached to the spacer. Thelocking mechanism attaches the device to the spinous processes ofadjacent vertebrae of the spine in a manner which is non-invasive withrespect to the vertebrae to which it is attached.

U.S. Pat. No. 5,092,889 (Forte) discloses an implant held in place bywrapping around the ribs to provide stabilization in compression ordistraction.

US Patent Publication Nos. 20090248076 (Reynolds) and 20090248079 (Kwak)each discloses an interspinous spacer having a pair of hooks that, uponlateral insertion between opposed spinous process, bear upon the opposedspinous processes.

SUMMARY OF THE INVENTION

The device of the present invention is intended for the treatment ofspinal stenosis. This device is an inter-spinous spacer that isintroduced through a single posterior incision. It uses a single pieceinsertion technique with a unilateral approach. The surgeon does notneed to access the opposite side of the spinous process. It allows theuser infinite adjustability in distraction height with a single lockingmechanism.

The implant of the present invention generally has four components:

-   -   a) Top body—for contacting the superior spinous process it        includes 1) a hook shaped portion with angled contact        surface, 2) a curved track with grooves to interface with the        grooves on the bottom body, and 3) insertion feature or hole;    -   b) Bottom body—for contacting the inferior spinous process it        includes 1) a hook shaped portion with angled contact        surface, 2) a curved track with grooves to interface with the        grooves on the top body, and 3) insertion feature or hole;    -   c) Housing—has a throughbore (or slot) that contains the curved        tracks of the top and bottom bodies as well as the set screw.        The housing further has a threaded recess that accepts a set        screw. The housing further has a mating feature (such as a pin)        to help constrain the tracks of the top and bottom bodies; and    -   d) Set screw—threads into the housing threaded recess and        compresses the curved track of the top and bottom bodies. The        set screw also has a mating feature (such as a pin) to help        constrain the tracks of the top and bottom bodies.

The device of the present invention has many advantages:

-   -   a) The implant's geometry allows for placement between the        spinous processes followed by distraction of the spinous        processes. In contrast, other conventional spinous process        implants distract the spinous processes while they are being        inserted.    -   b) Each of the body components of the device has an integrated        track with grooves to interface with the opposite body. The        advantage of the grooves is that it allows for infinite        adjustability. It also provides stability to the construct.    -   c) The curve of the track allows more distraction with a smaller        profile.

DESCRIPTION OF THE FIGURES

FIG. 1 discloses a top view of the present invention in the collapsedstate.

FIG. 2 discloses an insertion profile view of the present invention inthe collapsed state.

FIG. 3 discloses a top view of the present invention in the expandedstate.

FIG. 4 discloses an insertion profile view of the present invention inthe expanded state.

FIG. 5 discloses a pair of devices of the present invention implanted ona spine.

FIGS. 6 a and 6 b disclose an inserter of the present invention.

DETAILED DESCRIPTION

Referring now to FIGS. 1-4, there is provided an interspinous processdevice, comprising:

-   -   a) a first body 1, the first body comprising i) a first        hook-shaped portion 3 adapted for contacting a superior spinous        process, and ii) a first curved track portion 5 having a first        face 6 and a second face (not shown), the first face 6 having a        groove 8 therein and a rail 7 thereon running parallel to the        groove, the second face having a groove therein running parallel        to the groove of the first face;    -   b) a second body 11, the second body comprising i) a second        hook-shaped portion 13 adapted for contacting an inferior        spinous process, ii) a second curved track portion 15 having a        first face 16 and a second face (not shown), the first face 16        having a groove 17 therein, the second face having a groove        therein and a rail thereon,    -   c) a housing 21 having i) a slot 23 therethrough slidably        receiving the curved track portions, ii) a threaded throughhole        26 extending in a direction transverse to the slot, and a        containing pin (not shown) extending into the slot    -   d) a set screw 25 adapted for compressing the curved track        portions of the first and second bodies, the set screw having i)        a peripheral thread threadably received in the throughhole of        the housing, and ii) an end face (not shown) having a        constraining feature (such as a pin) adapted to constrain the        curved track portions,

-   wherein the rail and groove of the second face of the second body    respectively slidingly engage the groove and rail of the first face    of the first body,

-   wherein the groove of the first face of the second body slidingly    engages the constraining feature of the set screw, and

-   wherein the groove of the second face of the first body slidingly    engages the containing pin of the housing.

In some embodiments, each hook has an acutely angled face to moreclosely match the angle of the posterior-most portion of the spinousprocess it contacts. In contrast, the hooks of some conventional spinousprocess implants have a face that is perpendicular to the distractionpath. In the present invention, a first mating face 31 forms an acuteangle α which is less than 90 degrees with respect to the tips, whilethe second mating face 33 forms an obtuse angle β which is more than 90degrees with respect to the tips.

Therefore, in accordance with the present invention, there is providedan interspinous process device, comprising:

-   -   a) a first hook-shaped portion adapted for contacting a first        spinous process,    -   b) a second hook-shaped portion adapted for contacting a second        spinous process,    -   c) a connector portion adapted to adjustably connect the first        and second hook-shaped portions,

-   wherein the first hook-shaped portions has acutely angled contact    surface, and

-   wherein the second hook-shaped portion has an obtusely angled    contact surface.

In some embodiments, each track has an arc shape, which allows forincreasing the hook depth as distraction increases. Therefore, inaccordance with the present invention, there is provided an interspinousprocess device, comprising:

-   -   a) a first hook-shaped portion adapted for contacting a superior        spinous process,    -   b) a second hook-shaped portion adapted for contacting an        inferior spinous process,    -   c) an arced connector portion adapted to adjustably connect the        first and second hook-shaped portions.

In one arced embodiment, the arc forms a convex surface facing thehooked-shaped portions. In a second arced embodiment, the arc forms aconcave surface facing the hooked-shaped portions. In preferredembodiments, the arc defines a radius of between about 2 cm and about 5cm.

In preferred embodiments, the implant has a single locking mechanism.The requirement of only a single locking mechanism minimizes the amountof time the surgeon must spend stabilizing the device. Therefore, inaccordance with the present invention, there is provided an interspinousprocess device, comprising:

-   -   a) a first hook-shaped portion adapted for contacting a superior        spinous process,    -   b) a second hook-shaped portion adapted for contacting an        inferior spinous process,    -   c) a adjustable connector portion adapted to adjustably connect        the first and second hook-shaped portions,    -   d) a single lock (such as a set screw) adapted to lock the        adjustable connector portion.

In some embodiments, the set screw tightens upon an outer end portion ofeach track to produce an expanded hook state. In some embodiments, theinner end portion of each track is received in the housing to produce acollapsed hook state.

In some embodiments, each hook-shaped portion has an inflection point 35in each outer end portion. The inflection point allows the concave side37 of the hook tip 39 (i.e., the side of the tip associated with theconcave face 41 of the hook) to contact the spinous process duringinsertion. The geometry of these hooks allows their insertion betweenthe spinous processes without distracting the spinous processes. Thehooks' subsequent distraction (upon actuation of the inserter) producessimilar distraction in the spinous processes. In contrast, in otherconventional interspinous process spacers (which do not contain aninflection point), the convex portion of the hook tip (i.e., the side ofthe tip associated with the convex portion of the hook) distracts thespinous processes as the implant is being inserted. Therefore, theinflection point provides an advantage in that both hooks are passedbetween the spinous processes at the same time, thus insuring fullcapture of the spinous processes before distraction. Therefore, inaccordance with the present invention, there is provided an interspinousprocess device, comprising:

-   -   a) a first hook-shaped portion adapted for contacting a superior        spinous process,    -   b) a second hook-shaped portion adapted for contacting an        inferior spinous process,    -   c) a connector portion adapted to adjustably connect the first        and second hook-shaped portions,

-   wherein the first and second hook-shaped portions each have an    inflection point.

-   In addition, the tips are bulleted to more easily puncture the    ligament.

In some embodiments, at least one track has a longitudinal groove 7,17therein, and the tracks are oriented in the housing so that thelongitudinal grooves nest. Thus, each body component has an integratedtrack with grooves to interface with the opposite body. Therefore, inaccordance with the present invention, there is provided an interspinousprocess device, comprising:

-   -   a) a first hook-shaped portion adapted for contacting a superior        spinous process,    -   b) a second hook-shaped portion adapted for contacting an        inferior spinous process,    -   c) a connector portion adapted to adjustably connect the first        and second hook-shaped portions,        wherein the connector portion comprises first and second track        portions having mating grooves.

In some embodiments, the first and second bodies are oriented so thatthe hook-shaped portions open in opposite directions in the expandedstate.

In some embodiments, the housing has a mating feature to constrain thetracks in the housing. In particular, this mating feature is a pin thatprevents groove 17 from sliding all the way out of the housing, therebypreventing disassembly.

In some embodiments, the set screw has a mating feature to constrain thetracks in the housing. In particular, this mating feature is a pin thatprevents groove 17 from sliding all the way out of the housing, therebypreventing disassembly.

In some embodiments, the threaded recess extends into the housing in athird direction, and the throughbore extends through the housing in afourth direction substantially perpendicular to the third direction ofthe threaded recess.

In some embodiments, each body further comprises iii) an intermediateportion connecting the inner end portion of the first hook-shapedportion to the inner end portion of the first longitudinal track.

With correct material selection, the implant can be rigid for fusion, orhave a spring-like action for non-fusion applications.

FIG. 5 discloses a pair of devices 51 of the present invention implantedon a spine. The angled faces of the devices put the devices in anorientation that allows multiple implants to be implanted withoutcontacting each other.

FIGS. 6 a and 6 b disclose an inserter 61 of the present invention. Inparticular, the inserter comprises:

-   -   a) a longitudinal barrel 63 having a proximal end portion 65 and        a distal end portion 67,    -   b) a pistol grip 69 formed on the proximal end portion of the        barrel, the pistol grip having a lever 71, and    -   c) a shaft 73 disposed in the barrel and having a proximal end        portion 75 and a distal end portion 78 having a pair of teeth 80        extending therefrom,    -   d) a knob 77 formed on the proximal end portion of the knob, and    -   e) a pair of linkages 79 formed on the distal end portion 78 of        the shaft, each linkage having a distal pin 81.

Actuation of the lever on the inserter serves to distract the implant.

Actuation of the knob on the inserter serves to actuate the teeth tohold the housing.

In use, the pin components of the inserter fits into the insertionfeatures (holes) present on each of the bodies of the implant of thepresent invention. During insertion, the inserter is actuated so thatthe linkages are in an essentially parallel state and the pins arerelatively close together to reflect the collapsed state of the implant.During distraction, the inserter is actuated so that the linkages are inan essentially perpendicular state (as shown in FIGS. 6 a and 6 b) andthe pins are relatively far apart to reflect the expanded state of theimplant.

The components of the device of the present invention could be metal,plastic, or ceramic.

If a metal is chosen as the material of construction for a component,then the metal is preferably selected from the group consisting ofnitinol, titanium, titanium alloys (such as Ti-6Al-4V), chrome alloys(such as CrCo or Cr—Co—Mo) and stainless steel.

If a polymer is chosen as a material of construction for a component,then the polymer is preferably selected from the group consisting ofpolycarbonates, polyesters, (particularly aromatic esters such aspolyalkylene terephthalates, polyamides; polyalkenes; poly(vinylfluoride); PTFE; polyarylethyl ketone PAEK; and mixtures thereof.

In some embodiments, the components could be made of a stainless steelalloy, preferably BioDur^(R) CCM Plus^(R) Alloy available from CarpenterSpecialty Alloys, Carpenter Technology Corporation of Wyomissing, Pa. Insome embodiments, the component is made from a composite comprisingcarbon fiber. Composites comprising carbon fiber are advantageous inthat they typically have a strength and stiffness that is superior toneat polymer materials such as a polyarylethyl ketone PAEK. In someembodiments, the component is made from a polymer composite such as aPEKK-carbon fiber composite.

In some embodiments, the composite comprising carbon fiber furthercomprises a polymer. In some embodiments, the polymer is a polyarylethylketone (PAEK). In some embodiments, the PAEK is selected from the groupconsisting of polyetherether ketone (PEEK), polyether ketone ketone(PEKK) and polyether ketone (PEK). In some embodiments, the PAEK isPEEK.

In some embodiments, the carbon fiber comprises between 1 vol % and 60vol % (more preferably, between 10 vol % and 50 vol %) of the composite.In some embodiments, the polymer and carbon fibers are homogeneouslymixed. In others, the material is a laminate. In some embodiments, thecarbon fiber is present in a chopped state. In some embodiments, thechopped carbon fibers have a median length of between 1 mm and 12 mm,such as between 4.5 mm and 7.5 mm. In some embodiments, the carbon fiberis present as continuous strands.

In some embodiments, the composite comprises:

-   -   a) 40-99% (more preferably, 60-80 vol %) polyarylethyl ketone        (PAEK), and    -   b) 1-60% (more preferably, 20-40 vol %) carbon fiber,        wherein the polyarylethyl ketone (PAEK) is selected from the        group consisting of polyetherether ketone (PEEK), polyether        ketone ketone (PEKK) and polyether ketone (PEK).

In some embodiments, the composite consists essentially of PAEK andcarbon fiber. In some embodiments, the composite comprises 60-80 wt %PAEK and 20-40 wt % carbon fiber. For example, the composite maycomprise 65-75 wt % PAEK and 25-35 wt % carbon fiber.

1. An interspinous process device, comprising: a) a first body, thefirst body comprising i) a first hook-shaped portion adapted forcontacting a superior spinous process, and ii) a first track portionhaving a first groove therein, b) a second body, the second bodycomprising i) a second hook-shaped portion adapted for contacting aninferior spinous process, ii) a track portion having a groove therein,c) a housing having i) a slot therethrough slidably receiving the trackportions, ii) a threaded throughole extending in a direction transverseto the slot, d) a set screw adapted for compressing the track portionsof the first and second bodies, the set screw having i) a peripheralthread threadably received in the throughhole of the housing, whereinthe first and second bodies are slidingly received in the housing, andwherein the first body slidingly engages the second body.
 2. The deviceof claim 1 wherein the first hook shaped portion has a first angledcontact surface.
 3. The device of claim 1 wherein the first and secondbodies each comprise an insertion feature for connection to an inserterinstrument.
 4. The device of claim 3 wherein the first insertion featureis a hole.
 5. The device of claim 1 wherein the housing furthercomprises iii) a mating feature to help constrain the track portions andthe set screw further has ii) an end face having a constraining featureadapted to constrain the track portions.
 6. The device of claim 1wherein each hook-shaped portion has an inflection point.
 7. The deviceof claim 1 wherein the first hook-shaped portions has acutely angledcontact surface, and wherein the second hook-shaped portion has anobtusely angled contact surface.
 8. A method of using the interspinousprocess device of claim 1, the method comprising the steps of: a)inserting the hooked-shaped portions of the interspinous process deviceinto an interspinous space, b) expanding the interspinous processdevice.
 9. The method of claim 8 wherein the set screw tightens upon anouter end portion of each track to lock the interspinous process devicein an expanded hook state.
 10. The method of claim 8 wherein the firstand second bodies each have a geometry that allows their insertionbetween the spinous processes without distracting the spinous processes.11. An interspinous process spacer, comprising: a) a first bodycomprising i) a first hook-shaped portion having an outer end portionand an inner end portion, ii) a first longitudinal track having an outerend portion and an inner end portion, wherein the inner end portion ofthe first hook-shaped portion is connected to the inner end portion ofthe first longitudinal track, b) a second body comprising i) a secondhook-shaped portion having an outer end portion and an inner endportion, ii) a second longitudinal track having an outer end portion andan inner end portion, wherein the inner end portion of the secondhook-shaped portion is connected to the inner end portion of the secondlongitudinal track, c) a fixation housing having i) a threaded recessextending into the housing, and ii) a throughbore extending through thehousing to meet the threaded recess, d) a set screw received in thethreaded recess, wherein the first and second longitudinal tracks areslidably received in the throughbore in opposite directions.
 12. Thespacer of claim 11 wherein the set screw tightens upon an outer endportion of each track to produce an expanded hook state.
 13. The spacerof claim 12 wherein the inner end portion of each track is received inthe housing to produce a collapsed hook state.
 14. The spacer of claim11 wherein at least one track has a longitudinal groove therein, and thetracks are oriented in the housing so that the longitudinal groovesnest.
 15. The spacer of claim 11 wherein the first and second bodies areoriented so that the hook-shaped portions open in opposite directions inthe expanded state.
 16. The spacer of claim 11 wherein each track has acurved shape.
 17. The spacer of claim 11 wherein the housing has amating feature to constrain the tracks in the housing.
 18. The spacer ofclaim 11 wherein the set screw has a mating feature to constrain thetracks in the housing.
 19. The spacer of claim 11 wherein eachhook-shaped portion has an inflection point.
 20. The spacer of claim 11wherein the threaded recess extends into the housing in a thirddirection, and the throughbore extends through the housing in a fourthdirection substantially perpendicular to the third direction of thethreaded recess.
 21. The spacer of claim 11 wherein each body furthercomprises iii) an intermediate portion connecting the inner end portionof the first hook-shaped portion to the inner end portion of the firstlongitudinal track.
 22. An interspinous process device, comprising: a) afirst hook-shaped portion adapted for contacting a first spinous processand a having a tip, b) a second hook-shaped portion adapted forcontacting an second spinous process and a having a tip, c) a connectorportion adapted to adjustably connect the first and second hook-shapedportions, wherein the first hook-shaped portion has acutely angledcontact surface, and wherein the second hook-shaped portion has anobtusely angled contact surface, wherein the device has an expandedstate and a collapsed state, and wherein the tips contact each other inthe collapsed state.
 23. An interspinous process device, comprising: a)a first hook-shaped portion adapted for contacting a superior spinousprocess, b) a second hook-shaped portion adapted for contacting aninferior spinous process, c) an arced connector portion adapted toadjustably connect the first and second hook-shaped portions, whereinthe arced connector portion forms a convex surface facing thehooked-shaped portions.
 24. An interspinous process device, comprising:a) a first hook-shaped portion having a concave face adapted forcontacting a superior spinous process and a tip, b) a second hook-shapedportion having a concave face adapted for contacting an inferior spinousprocess and a tip, c) a connector portion adapted to adjustably connectthe first and second hook-shaped portions, wherein the first and secondhook-shaped portions each have an inflection point between its concaveface and its tip.
 25. An interspinous process device, comprising: a) afirst hook-shaped portion adapted for contacting a superior spinousprocess, b) a second hook-shaped portion adapted for contacting aninferior spinous process, c) a connector portion adapted to adjustablyconnect the first and second hook-shaped portions, wherein the connectorportion comprises first and second track portions having mating grooves.